This invention relates to the structure of electronic devices, such as capacitors and transistors, embodying a thin film which has been grown upon a semiconductor substrate and more particularly is concerned with the electrical characteristics of such structures when embodied in electronic devices.
We have described in our prior U.S. patents, such as U.S. Pat. No. 5,830,270, various processes for constructing thin films upon a semiconductor substrate with few, if any, dislocations or other undesirable defects at the thin-film/substrate interface. Some of our construction processes involve a layer-by-layer build up of an epitaxial, and sometimes commensurate, oxide upon the substrate (i.e., a crystalline oxide-on-semiconductor substrate, or COS, structure) wherein each layer in the build up process is comprised of a constituent plane of the oxide. For example, in our U.S. Pat. No. 5,830,270, we describe a build-up of a perovskite oxide upon a substrate as having the general formula (AO)n(Axe2x80x2BO3)m wherein which n and m are the non-negative integer repeats of single oxide layers. The element O in the formula represents oxygen, while the element A (or Axe2x80x2) can be a material found in Group IA, IIA or IVB of the periodic table of elements and the element B can be a material found in Group III, IVA or VA of the periodic table of elements. Moreover, the composition of each element A (or Axe2x80x2) or B is not limited to a single material, but instead can be comprised of a mixture or alloy of materials.
While perfecting techniques to construct crystalline oxide-on-semiconductor (COS) structures, however, little attention has been given to the electrical behavioral characteristics of electronic devices within which such COS structures are embodied. It would be desirable to provide a COS structure for use in an electronic device wherein the physical structure, or physical characteristics, of the COS structure impart desired electrical structure, or electrical behavioral characteristics to the structure.
Accordingly, it is an object of the present invention to provide such a COS structure which is physically constructed so that desired, or predetermined, electrical structure is imparted to the COS structure and an associated method of making such a structure.
Another object of the present invention is to provide such a COS structure whose construction is controlled to impart a desired, or predetermined, band offset parameter to the structure.
A further object of the present invention is to provide such a structure which incorporates a perovskite oxide for the gate oxide of an electronic device and wherein the band gap at the oxide/substrate interface is relatively small.
A still further object of the present invention is to provide a method of making such a structure wherein the deposition steps are carried out at low temperature (e.g. between room temperature and 400xc2x0 C.).
This invention resides in a crystalline oxide-on-semiconductor structure and a process for making the structure.
The crystalline oxide-on-semiconductor structure includes a semiconductor-based substrate and an epitaxial thin film overlying the surface of the substrate wherein the thin film consists of a first stratum of single atomic layers of an alkaline earth oxide (AO) and a second stratum of single unit cell layers of an oxide material (Axe2x80x2BO3) so that the multilayer thin film arranged upon the substrate surface can be designated (AO)n(Axe2x80x2BO3)m wherein n is an integer repeat of single atomic layers of the AO alkaline earth oxide and m is an integer repeat of unit cell layers of the Axe2x80x2BO3 oxide material. In addition, the values of n and m in the general formula of the thin film have been selected to provide the physical structure of the structure with a desired, or predetermined, electrical structure, or characteristic, at the substrate/thin film interface.
In the process for making the structure of the invention, the values of n and m are selected prior to the build up of n layers of AO alkaline earth oxide and m layers of the Axe2x80x2BO3 oxide material upon the substrate so that the resultant crystalline oxide thin film is provided with predetermined electrical characteristics at the substrate/thin-film interface.